The yeast will make a difference one way or the other, but I think 1,020 is a more realistic FG for this recipe.

Firstly, the beer is pretty big with an OG of 1.070 (I assume), so at 70-75% attenuation, which was typical for me when I used extract, we're talking about 1.017-1.021. Maybe higher, depending on the brand.

Also, I know I harp on this, but the more Crystal Malt you use, the more unfermentables you'll add. I've read that each pound decreases your attenuation by 2%, so the 1.5# you used would bring you in line with your 1.023 FG.

1728 is a low attenuator at 69-7%. 1.023 FG from 1.080 OG is 71% attenuation, so it looks like the yeast hit right in the middle of it's range.

If you want to make a drier beer from extract, without reducing the amount of Crystal Malt, you need to replace some of the DME with about an equal weight of table sugar or corn sugar. That will replace some of the partially fermentable extract with fully fermentable sugar, giving you a lower FG. Using sugar to lighten the body has been a common technique among British and Belgian breweries.